1. FIELD OF THE INVENTION
The present invention relates generally to plant molecular biology and genetic engineering and more specifically to the production of genetically modified seed plants in which the natural process of dehiscence is delayed.
2. BACKGROUND INFORMATION
Rapeseed is one of the most important oilseed crops after soybeans and cottonseed, representing 10% of the world oilseed production in 1990. Rapeseed contains 40% oil, which is pressed from the seed, leaving a high-protein seed meal of value for animal feed and nitrogen fertilizer. Rapeseed oil, also known as canola oil, is a valuable product, representing the fourth most commonly traded vegetable oil in the world.
The production of oilseeds, meal and oil from rapeseed plants has been increasing continuously for the last 30 years for food and feed grains, mainly by expansion of the area under cultivation. Most northern European countries produce rapeseed as their main edible oil crop. By the year 2000, China is expected to be the leading producer with 9.2 metric tons (Mt; 26%); followed by India with 7.8 Mt (22%); the European Community (12 countries), with 7.6 Mt (21%); Canada, 3.8 Mt (11%) and eastern Europe with 2.6 Mt (7%).
Unfortunately, the yield of seed from rapeseed and related plants is limited by pod dehiscence, which is a process that occurs late in fruit development whereby the pod is opened and the enclosed seeds released. Degradation and separation of cell walls along a discrete layer of cells dividing the two halves of the pod, termed the "dehiscence zone," result in separation of the two halves of the pod and release of the contained seeds. Seed "shattering," whereby seeds are prematurely shed through dehiscence before the crop can be harvested, is a significant problem faced by commercial seed producers and represents a loss of income to the industry. Adverse weather conditions can exacerbate the process of dehiscence, resulting in greater than 50% loss of seed yield.
Attempts to solve this problem over the past 20 years have focused on the breeding of shatter-resistant varieties. However, these plant hybrids are frequently sterile and lose favorable characteristics that must be regained by backcrossing, which is both time-consuming and laborious. Other strategies to alleviate pod shattering include the use of chemicals such as pod sealants or mechanical techniques such as swathing to reduce wind-stimulated shattering. To date, however, a simple method for producing genetically modified seed plants that do not open and release their seeds prematurely has not been described.
Thus, a need exists for identifying genes that regulate the dehiscence process and for developing genetically modified seed plant varieties in which the natural seed dispersal process is delayed. The present invention satisfies this need and provides related advantages as well.